As the United States and its allies -- including Australia -- move closer to intervening in the Syrian civil war, more questions are emerging over the chemical weapons attack which is the pretext for that intervention. Challenging questions are being asked about the motive behind the attack, as well as the consequences of a response to it.

The US has been reluctant to intervene in the Syrian conflict, yet drawn a "red line" which, if crossed, would trigger an intervention. The question now being asked is why Syrian dictator Bashar al-Assad would unnecessarily provoke the US into a response?

Assad knew that, once publicly committed, the US could not back down from its threat to intervene. For US President Barack Obama to make such a threat and then not carry it through would weaken its international status and prompt further possible tests of its strategic resolve.

The evidence, too, is that despite the huge cost in civilian lives, the Assad regime is at least holding its own in the civil war and has made recent gains. These gains have been largely due to logistical support from Russia, China and Iran, and the intervention of Hezbollah fighters from neighbouring Lebanon.

This, then, begs the questions of why it would resort to using chemical weapons when there is no pressing need to do so, and especially knowing it would engender an external military response?

The Assad regime being evil is a morally satisfying but intellectually bereft answer to this question that does not transcend reasonable -- and growing -- doubt. It is certain that chemical weapons have been used in Syria, but that is the extent of the facts.

It is possible that the order for Assad regime forces to use its chemical weapons did not come from Assad himself. A rogue commander could have used the weapons, for reasons that can only be guessed at.

But looking at who has most to gain from such an attack, suspicion falls less on the Assad regime and more on the faltering anti-Assad rebellion. External intervention could, at least initially, tip the balance of power in Syria’s civil war in favour of the anti-Assad forces.

The Assad regime's reluctance and delay in allowing in UN weapons inspectors has not helped allay suspicion that the chemical weapons attach was a deliberate act. However, had a local commander given the order, Assad would have been aware of the likely consequences and thus attempted to delay formal investigations in order to allow signs of the chemicals to dissipate.

Of the two main opposition groupings, the more secular (and Western-supported) Free Syrian Army has struggled and has the most to gain from external intervention. The Saudi and Qatar-backed and Al Qaeda-linked al Nusra Front and the Syrian Islamic Front, though, would also benefit from external intervention. If intervention helped topple the Assad regime, it would ease the way towards them establishing an Islamist state.

While there is no evidence that either of these two somewhat disparate groupings are responsible for the chemical attack, one is clearly desperate and the other has, during the civil war, demonstrated its own lack of moral compunction. The hard evidence, then, beyond the simple fact of an attack, remains ambiguous.

Apart from the formal legality of a direct external intervention, careful consideration is being given to how much evidence will be needed to launch a US-led attack. There appears little ulterior reason for the US to want to intervene in the Syrian civil war, given that it is only likely to further stir up the hornets’ nest.

The US is being drawn into the Syrian civil war in a seemingly mechanistic way. Yet there remains no hard evidence as to who was the perpetrator of the chemical attack. This level of uncertainty has echoes similar to that of Iraq's "weapons of mass destruction", and the continuing disaster that remains what is left of the Iraqi state.